Can Fox 34 be adjusted to 100mm?

It can, with some spacers. This particular mod is not FOX-approved, but it can be done. The most notable side effect of this is a lack of end-stroke ramp up. The full list of what FOX approves in terms of Float travel adjustment can be found here: 2013 Float 130 - 180 Travel Adjust

Notably, there is an Excel spreadsheet linked to on that page (direct link here - http://service.foxracingshox.com/con...assemblies.xls) that contains all the part numbers and combinations that FOX offer for reducing your travel. Reducing your travel that drastically however (given the minimum approved is 130mm), means that the compression ratio (ratio of volume at topout vs volume at bottom out) is also greatly reduced, which means that you need to adjust the fork's volume accordingly, in addition to using a suitable spring spacer. We have successfully spaced down 140mm forks as low as 100mm, but once again, be aware that if you aren't careful with how you go about it, there can be undesirable side effects including excessive bottoming out, knocking at topout or damage to your negative spring assembly.